We present ASCA observations of the radio-selected BL Lacertae objects 1749+096 ( z =0.32 ) and 2200+420 ( BL Lac , z =0.069 ) performed in 1995 September and November , respectively .
The ASCA spectra of both sources can be described as a first approximation by a power law with photon index \Gamma \approx 2 .
This is flatter than for most X-ray-selected BL Lacs observed with ASCA , in agreement with the predictions of current blazar unification models .
While 1749+096 exhibits tentative evidence for spectral flattening at low energies , a concave continuum is detected for 2200+420 : the steep low-energy component is consistent the high-energy tail of the synchrotron emission responsible for the longer wavelengths , while the harder tail at higher energies is the onset of the Compton component .
The two BL Lacs were observed with ground-based telescopes from radio to TeV energies contemporaneously with ASCA .
The spectral energy distributions are consistent with synchrotron-self Compton emission from a single homogeneous region shortward of the IR/optical wavelengths , with a second component in the radio domain related to a more extended emission region .
For 2200+420 , comparing the 1995 November state with the optical/GeV flare of 1997 July , we find that models requiring inverse Compton scattering of external photons provide a viable mechanism for the production of the highest ( GeV ) energies during the flare .
In particular , an increase of the external radiation density and of the power injected in the jet can reproduce the flat \gamma -ray continuum observed in 1997 July .
A directly testable prediction of this model is that the line luminosity in 2200+420 should vary shortly after ( \sim 1 month ) a non-thermal synchrotron flare .